front two curtain bangs get wayy too oily, greasy and look horrible

I have frizzy,thick and wavy hair. I usually try to straighten it since its more manageable and lasts me a couple of days. However, when tying my hair, i like to leave the front two strands (curtain bangs out) they become really greasy and way too thin from straightening, they hold no shape and wave out in different ways. What can I do?